The present invention relates to a thermal transfer image-receiving sheet and more particularly to a thermal transfer image-receiving sheet which exhibits an excellent releasability in the thermal transfer.
Various thermal transfer printing processes are known in the art. One of them is a transfer printing process which comprises supporting a sublimable dye as a recording agent on a substrate sheet, such as a plastic film, to form a thermal transfer sheet and forming various full color images on a dye-receiving layer provided on paper, a plastic film or the like.
In this case, a thermal head of a printer is used as heating means, and a number of color dots of three or four colors are transferred to the thermal transfer image-receiving sheet, thereby reproducing a full color image of an original by means of the multicolor dots.
The above-described thermal transfer process have problems, such as fusing of the thermal transfer sheet and the thermal transfer sheet-receiving sheet to render peeling of both the sheets from each other difficult or to deteriorate the formed image, due to the nature of the process wherein, in the formation of an image, the thermal transfer sheet and thermal transfer image-receiving sheet are put on top of each other with the dye layer of the thermal transfer sheet facing the dye-receiving layer of the thermal transfer image-receiving sheet and both the dye layer and the dye-receiving layer comprise a thermoplastic resin.
In order to solve the above-described problems, a proposal has been made on the addition of a release agent to the dye-receiving layer to bleed out the release agent on the surface of the dye-image receiving layer, thereby forming a release layer.
In this method, when use is made of liquid or wax release agents, they unfavorably contaminate other materials or give rise to discoloration of the image. For this reason, the use of a reactive curing release agent as the release agent has been proposed.
According to this method, after the formation of a dye-receiving layer, heat treatment is effected to bleed out a release agent contained in the dye-receiving layer on the surface of the dye-receiving layer to form a crosslinked thin film of the release agent on the surface of the dye-receiving layer. However, a long period of time is required for the crosslinking reaction, which lowers the productivity. Further, the coating strength of the crosslinked film is so low that the scratch resistance is unsatisfactory. Japanese Patent Laid-Open No. 87424/1991 describes examples of reactive silicones. In these reactive silicones, a reaction should occur between vinyl groups that unfavorably have a low reactivity. Moreover, an image-receiving material comprising an image-receiving layer and a particular silicone crosslinked film provided on the surface of the image-receiving layer is also known in the art (see Japanese Patent Laid-Open No. 116189/1987). This image-receiving material, however, is not always satisfactory.
Accordingly, an object of the present invention is to provide a thermal transfer image-receiving sheet having a dye-receiving layer which is excellent in reaction rate of the release agent, coating strength of the release layer and releasability of the thermal transfer sheet.